A DOD telephony trunk is a typical means to connect a Private Automatic Branch Exchange (PABX) system to a Central Office (CO). At the PABX, a trunk card (TC) is typically employed to emulate the functionality of a telephone. A PABX controller uses the TC to transmit to and receive from the CO DC and AC signals.
One function of the TC is to monitor the telephone loop and extract DC signalling information therefrom. However, the nature of the DC signals varies from country to country and thus normally requires separate and complex dedicated TC circuitry to be provided for each country. Because of this, many conventional TC implementations are country-specific. As a result, additional cost and complexity is incurred in order to internationally distribute telephony equipment which includes a TC.
It is therefore one object of the invention to provide a single TC circuit which receives and processes a variety of country-specific DC telephone loop signals.